fdisk
FDISK(8) System Administration FDISK(8)
NAME
fdisk - manipulate disk partition table
SYNOPSIS
fdisk [options] device
fdisk -l [device...]
DESCRIPTION
fdisk is a dialog-driven program for creation and manipulation of par-
tition tables. It understands GPT, MBR, Sun, SGI and BSD partition ta-
bles.
Block devices can be divided into one or more logical disks called par-
titions. This division is recorded in the partition table, usually
found in sector 0 of the disk. (In the BSD world one talks about `disk
slices' and a `disklabel'.)
All partitioning is driven by device I/O limits (the topology) by de-
fault. fdisk is able to optimize the disk layout for a 4K-sector size
and use an alignment offset on modern devices for MBR and GPT. It is
always a good idea to follow fdisk's defaults as the default values
(e.g. first and last partition sectors) and partition sizes specified
by the +/-<size>{M,G,...} notation are always aligned according to the
device properties.
CHS (Cylinder-Head-Sector) addressing is deprecated and not used by de-
fault. Please, do not follow old articles and recommendations with
"fdisk -S <n> -H <n>" advices for SSD or 4K-sector devices.
Note that partx(8) provides a rich interface for scripts to print disk
layouts, fdisk is mostly designed for humans. Backward compatibility
in the output of fdisk is not guaranteed. The input (the commands)
should always be backward compatible.
OPTIONS
-b, --sector-size sectorsize
Specify the sector size of the disk. Valid values are 512,
1024, 2048, and 4096. (Recent kernels know the sector size.
Use this option only on old kernels or to override the kernel's
ideas.) Since util-linux-2.17, fdisk differentiates between
logical and physical sector size. This option changes both sec-
tor sizes to sectorsize.
-B, --protect-boot
Don't erase the begin of the first disk sector when create a new
disk label. This feature is supported for GPT and MBR.
-c, --compatibility[=mode]
Specify the compatibility mode, 'dos' or 'nondos'. The default
is non-DOS mode. For backward compatibility, it is possible to
use the option without the mode argument -- then the default is
used. Note that the optional mode argument cannot be separated
from the -c option by a space, the correct form is for example
'-c=dos'.
-h, --help
Display a help text and exit.
-L, --color[=when]
Colorize the output. The optional argument when can be auto,
never or always. If the when argument is omitted, it defaults
to auto. The colors can be disabled; for the current built-in
default see the --help output. See also the COLORS section.
-l, --list
List the partition tables for the specified devices and then
exit. If no devices are given, those mentioned in /proc/parti-
tions (if that file exists) are used.
-o, --output list
Specify which output columns to print. Use --help to get a list
of all supported columns.
The default list of columns may be extended if list is specified
in the format +list (e.g. -o +UUID).
-s, --getsz
Print the size in 512-byte sectors of each given block device.
This option is DEPRECATED in favour of blockdev(1).
-t, --type type
Enable support only for disklabels of the specified type, and
disable support for all other types.
-u, --units[=unit]
When listing partition tables, show sizes in 'sectors' or in
'cylinders'. The default is to show sizes in sectors. For
backward compatibility, it is possible to use the option without
the unit argument -- then the default is used. Note that the
optional unit argument cannot be separated from the -u option by
a space, the correct form is for example '-u=cylinders'.
-C, --cylinders number
Specify the number of cylinders of the disk. I have no idea why
anybody would want to do so.
-H, --heads number
Specify the number of heads of the disk. (Not the physical num-
ber, of course, but the number used for partition tables.) Rea-
sonable values are 255 and 16.
-S, --sectors number
Specify the number of sectors per track of the disk. (Not the
physical number, of course, but the number used for partition
tables.) A reasonable value is 63.
-w, --wipe when
Wipe filesystem, RAID and partition-table signatures from the
device, in order to avoid possible collisions. The argument
when can be auto, never or always. When this option is not
given, the default is auto, in which case signatures are wiped
only when in interactive mode. In all cases detected signatures
are reported by warning messages before a new partition table is
created. See also wipefs(8) command.
-W, --wipe-partition when
Wipe filesystem, RAID and partition-table signatures from a
newly created partitions, in order to avoid possible collisions.
The argument when can be auto, never or always. When this op-
tion is not given, the default is auto, in which case signatures
are wiped only when in interactive mode and after confirmation
by user. In all cases detected signatures are reported by warn-
ing messages before a new partition is created. See also
wipefs(8) command.
-V, --version
Display version information and exit.
DEVICES
The device is usually /dev/sda, /dev/sdb or so. A device name refers
to the entire disk. Old systems without libata (a library used inside
the Linux kernel to support ATA host controllers and devices) make a
difference between IDE and SCSI disks. In such cases the device name
will be /dev/hd* (IDE) or /dev/sd* (SCSI).
The partition is a device name followed by a partition number. For ex-
ample, /dev/sda1 is the first partition on the first hard disk in the
system. See also Linux kernel documentation (the Documentation/de-
vices.txt file).
SIZES
The "last sector" dialog accepts partition size specified by number of
sectors or by +/-<size>{K,B,M,G,...} notation.
If the size is prefixed by '+' then it is interpreted as relative to
the partition first sector. If the size is prefixed by '-' then it is
interpreted as relative to the high limit (last available sector for
the partition).
In the case the size is specified in bytes than the number may be fol-
lowed by the multiplicative suffixes KiB=1024, MiB=1024*1024, and so on
for GiB, TiB, PiB, EiB, ZiB and YiB. The "iB" is optional, e.g. "K" has
the same meaning as "KiB".
The relative sizes are always aligned according to device I/O limits.
The +/-<size>{K,B,M,G,...} notation is recommended.
For backward compatibility fdisk also accepts the suffixes KB=1000,
MB=1000*1000, and so on for GB, TB, PB, EB, ZB and YB. These 10^N suf-
fixes are deprecated.
SCRIPT FILES
fdisk allows to read (by 'I' command) sfdisk compatible script files.
The script is applied to in-memory partition table, and then it is pos-
sible to modify the partition table before you write it to the device.
And vice-versa it is possible to write the current in-memory disk lay-
out to the script file by command 'O'.
The script files are compatible between cfdisk, sfdisk, fdisk and an-
other libfdisk applications. For more details see sfdisk(8).
DISK LABELS
GPT (GUID Partition Table)
GPT is modern standard for the layout of the partition table.
GPT uses 64-bit logical block addresses, checksums, UUIDs and
names for partitions and an unlimited number of partitions (al-
though the number of partitions is usually restricted to 128 in
many partitioning tools).
Note that the first sector is still reserved for a protective
MBR in the GPT specification. It prevents MBR-only partitioning
tools from mis-recognizing and overwriting GPT disks.
GPT is always a better choice than MBR, especially on modern
hardware with a UEFI boot loader.
DOS-type (MBR)
A DOS-type partition table can describe an unlimited number of
partitions. In sector 0 there is room for the description of 4
partitions (called `primary'). One of these may be an extended
partition; this is a box holding logical partitions, with de-
scriptors found in a linked list of sectors, each preceding the
corresponding logical partitions. The four primary partitions,
present or not, get numbers 1-4. Logical partitions are num-
bered starting from 5.
In a DOS-type partition table the starting offset and the size
of each partition is stored in two ways: as an absolute number
of sectors (given in 32 bits), and as a Cylinders/Heads/Sectors
triple (given in 10+8+6 bits). The former is OK -- with
512-byte sectors this will work up to 2 TB. The latter has two
problems. First, these C/H/S fields can be filled only when the
number of heads and the number of sectors per track are known.
And second, even if we know what these numbers should be, the 24
bits that are available do not suffice. DOS uses C/H/S only,
Windows uses both, Linux never uses C/H/S. The C/H/S addressing
is deprecated and may be unsupported in some later fdisk ver-
sion.
Please, read the DOS-mode section if you want DOS-compatible
partitions. fdisk does not care about cylinder boundaries by
default.
BSD/Sun-type
A BSD/Sun disklabel can describe 8 partitions, the third of
which should be a `whole disk' partition. Do not start a parti-
tion that actually uses its first sector (like a swap partition)
at cylinder 0, since that will destroy the disklabel. Note that
a BSD label is usually nested within a DOS partition.
IRIX/SGI-type
An IRIX/SGI disklabel can describe 16 partitions, the eleventh
of which should be an entire `volume' partition, while the ninth
should be labeled `volume header'. The volume header will also
cover the partition table, i.e., it starts at block zero and ex-
tends by default over five cylinders. The remaining space in
the volume header may be used by header directory entries. No
partitions may overlap with the volume header. Also do not
change its type or make some filesystem on it, since you will
lose the partition table. Use this type of label only when
working with Linux on IRIX/SGI machines or IRIX/SGI disks under
Linux.
A sync() and an ioctl(BLKRRPART) (rereading the partition table from
disk) are performed before exiting when the partition table has been
updated.
DOS mode and DOS 6.x WARNING
Note that all this is deprecated. You don't have to care about things
like geometry and cylinders on modern operating systems. If you really
want DOS-compatible partitioning then you have to enable DOS mode and
cylinder units by using the '-c=dos -u=cylinders' fdisk command-line
options.
The DOS 6.x FORMAT command looks for some information in the first sec-
tor of the data area of the partition, and treats this information as
more reliable than the information in the partition table. DOS FORMAT
expects DOS FDISK to clear the first 512 bytes of the data area of a
partition whenever a size change occurs. DOS FORMAT will look at this
extra information even if the /U flag is given -- we consider this a
bug in DOS FORMAT and DOS FDISK.
The bottom line is that if you use fdisk or cfdisk to change the size
of a DOS partition table entry, then you must also use dd(1) to zero
the first 512 bytes of that partition before using DOS FORMAT to format
the partition. For example, if you were using fdisk to make a DOS par-
tition table entry for /dev/sda1, then (after exiting fdisk and reboot-
ing Linux so that the partition table information is valid) you would
use the command "dd if=/dev/zero of=/dev/sda1 bs=512 count=1" to zero
the first 512 bytes of the partition.
fdisk usually obtains the disk geometry automatically. This is not
necessarily the physical disk geometry (indeed, modern disks do not re-
ally have anything like a physical geometry, certainly not something
that can be described in the simplistic Cylinders/Heads/Sectors form),
but it is the disk geometry that MS-DOS uses for the partition table.
Usually all goes well by default, and there are no problems if Linux is
the only system on the disk. However, if the disk has to be shared
with other operating systems, it is often a good idea to let an fdisk
from another operating system make at least one partition. When Linux
boots it looks at the partition table, and tries to deduce what (fake)
geometry is required for good cooperation with other systems.
Whenever a partition table is printed out in DOS mode, a consistency
check is performed on the partition table entries. This check verifies
that the physical and logical start and end points are identical, and
that each partition starts and ends on a cylinder boundary (except for
the first partition).
Some versions of MS-DOS create a first partition which does not begin
on a cylinder boundary, but on sector 2 of the first cylinder. Parti-
tions beginning in cylinder 1 cannot begin on a cylinder boundary, but
this is unlikely to cause difficulty unless you have OS/2 on your ma-
chine.
For best results, you should always use an OS-specific partition table
program. For example, you should make DOS partitions with the DOS
FDISK program and Linux partitions with the Linux fdisk or Linux cfdisk
programs.
COLORS
Implicit coloring can be disabled by an empty file /etc/terminal-col-
ors.d/fdisk.disable.
See terminal-colors.d(5) for more details about colorization configura-
tion. The logical color names supported by fdisk are:
header The header of the output tables.
help-title
The help section titles.
warn The warning messages.
welcome
The welcome message.
AUTHORS
Karel Zak <kzak@redhat.com>
Davidlohr Bueso <dave@gnu.org>
The original version was written by Andries E. Brouwer, A. V. Le Blanc
and others.
ENVIRONMENT
FDISK_DEBUG=all
enables fdisk debug output.
LIBFDISK_DEBUG=all
enables libfdisk debug output.
LIBBLKID_DEBUG=all
enables libblkid debug output.
LIBSMARTCOLS_DEBUG=all
enables libsmartcols debug output.
LIBSMARTCOLS_DEBUG_PADDING=on
use visible padding characters. Requires enabled LIBSMART-
COLS_DEBUG.
SEE ALSO
cfdisk(8), mkfs(8), partx(8), sfdisk(8)
AVAILABILITY
The fdisk command is part of the util-linux package and is available
from https://www.kernel.org/pub/linux/utils/util-linux/.
util-linux February 2016 FDISK(8)
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